Fix test to work with remote-test-server.

remote-test-server does not set the current_dir, and leaves it
as `/`.

src/test/ui/command/command-current-dir.rs

@@ -16,8 +16,14 @@ fn main() {
         std::process::exit(0);
     }
     let exe = me.file_name().unwrap();
-    let cwd = std::env::current_dir().unwrap();
+    let cwd = me.parent().unwrap();
     eprintln!("cwd={:?}", cwd);
+    // Change directory to where the exectuable is located, since this test
+    // fundamentally needs to use relative paths. In some cases (like
+    // remote-test-server), the current_dir can be somewhere else, so make
+    // sure it is something we can use. We assume we can write to this
+    // directory.
+    env::set_current_dir(&cwd).unwrap();
     let foo = cwd.join("foo");
     let bar = cwd.join("bar");
     fs::create_dir_all(&foo).unwrap();